TORONTO -- A drug for severe osteoporosis has an unexpected side effect, researchers found -- it appears to speed healing of hard-to-mend bone fractures.

TORONTO, April 16 -- A drug for severe osteoporosis has an unexpected side effect, researchers found -- it appears to speed healing of hard-to-mend bone fractures.

In an observational study of 145 patients with slow-to-heal fractures, 93% had complete recovery within 12 weeks of starting treatment with teriparatide (Forteo), according to Susan Bukata, M.D., of the University of Rochester Medical Center in Rochester, N.Y.

Half of the patients had spent at least six months in pain with a fracture that would not heal and others had either been in that position or were elderly and likely to need surgical intervention for their fractures, Dr. Bukata and colleagues reported earlier this year at a conference.

The observations were strong enough to warrant a full-scale randomized trial in patients with pelvic fractures, now starting at the university, officials said in a release.

"It takes three to four months for a typical pelvic fracture to heal," Dr. Bukata said in a statement. "But during those three months, patients can be in excruciating pain, because there are no medical devices or other treatments that can provide relief to the patient."

The original research suggests that period might be sharply reduced, she said. "Imagine if we can give patients a way to cut the time of their pain and immobility in half? That's what teriparatide did in our initial research," she said.

Teriparatide is a fragment of parathyroid hormone that contains 34 amino acids rather than the 84 found in the naturally occurring substance. Animal studies have shown that the drug speeds bone healing at daily doses of between 10 and 40 micrograms per kilogram of body weight.

One of the key findings of the original study is that the standard dose of teriparatide -- 20 micrograms a day, which for a 70-kilogram (154 lb) patient translates to only 0.29 micrograms per kilogram -- had the same effect.

In the study, all patients tolerated the drug without complications, the researchers reported, although three stopped early because they did not like giving themselves daily injections. Two of those patients had, in fact, already healed their fracture.

Within 12 weeks of starting treatment, 141 of the 145 patients no longer had pain at the fracture site, 135 had radiographic and clinical union of their fractures, and six had partial union of their fractures that clinically functioned as a healed fracture.

Only four had no improvement in pain or fracture union.

The study was observational, retrospectively analyzing medical records and radiographs, the researchers noted.

According to Edward Puzas, Ph.D., the principal investigator of the new pelvic-fracture trial, teriparatide significantly speeds up fracture healing by changing the behavior and number of the cartilage and the bone stem cells involved in the process.

"Teriparatide dramatically stimulates the bone's stem cells into action," Dr. Puzas said in a statement.

"As a result, the callus forms quicker and stronger. Osteoblasts form more bone and the micromotion associated with the fracture is more rapidly eliminated," he said.

The drug is not inexpensive -- about $800 a week -- but Dr. Bukata said treatment can be cost-effective. For older patients, she said, a slow-to-heal fracture might mean spending a few weeks in a nursing home.

If the patient's stay could be reduced by a week, "that would pay for the drugs," Dr. Bukata told reporters.

Dr. Bukata said the study began when she saw that painful bone fractures in osteoporotic patients healed within a few months of taking teriparatide.

"I had patients with severe osteoporosis, in tremendous pain from multiple fractures throughout their spine and pelvis, who I would put on teriparatide," she said.

"When they would come back for their follow-up visits three months later," she said, "it was amazing to see not just the significant healing in their fractures, but to realize they were pain-free."

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